POJ 3463

  题目意思就是要求s到t的最短路径个数和s到t的次短路径个数。

 参考了大佬的博客

#include<iostream>
#include<string.h>
#include<queue>
#include<stdio.h>
using namespace std;
#define inf 0x3f3f3f3f
int n,m,en,st,et;
int head[1010];
int dis[1010][2];
int cnt[1010][2];
int vis[1010][2];
struct edge
{
    int from,to;
    int dis;
    int next;
}edge[10005];
struct node
{
    int v;
    int flag;
    node(int a,int b)
    {
        v=a;
        flag=b;
    }


};
struct cmp
{
    bool operator()(struct node a,struct node b)
    {

        return dis[a.v][a.flag]>dis[b.v][b.flag];    //表示按结构体变量里的x成员为比较要素，升序排列
    }
};
int dijkstra()
{
    memset(vis,0,sizeof(vis));
    memset(cnt,0,sizeof(cnt));
    for(int i=1;i<=n;i++)
        dis[i][0]=dis[i][1]=inf;
    priority_queue<struct node,vector<struct node>,cmp>q;
    q.push(node(st,0));
    dis[st][0]=0;
    cnt[st][0]=1;
    while(!q.empty())
    {
        node top=q.top();
        q.pop();
        int v=top.v;
        int flag=top.flag;
        if(vis[v][flag])
            continue;
        vis[v][flag]=1;
        for(int i=head[v];i!=-1;i=edge[i].next)
        {
            int to=edge[i].to;
            int dist=dis[v][flag]+edge[i].dis;
            if(dist<dis[to][0])
            {
                if(dis[to][0]!=inf)
                {
                    dis[to][1]=dis[to][0];
                    cnt[to][1]=cnt[to][0];
                    q.push(node(to,1));
                }
                dis[to][0]=dist;
                cnt[to][0]=cnt[v][flag];
                q.push(node(to,0));
            }
            else
                if(dist==dis[to][0])
                    cnt[to][0]+=cnt[v][flag];
            else
                if(dist<dis[to][1])
                {
                    dis[to][1]=dist;
                    cnt[to][1]=cnt[v][flag];
                    q.push(node(to,1));

                }
                else
                    if(dist==dis[to][1])
                    {
                        cnt[to][1]+=cnt[v][flag];

                    }


        }
    }
    if(dis[et][0]+1==dis[et][1])
        return cnt[et][0]+cnt[et][1];
    return cnt[et][0];
}

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        en=0;
        memset(head,-1,sizeof(head));
        scanf("%d%d",&n,&m);
        while(m--)
        {
            int a,b,c;
            scanf("%d%d%d",&a,&b,&c);
            edge[en].from=a;
            edge[en].to=b;
            edge[en].dis=c;
            edge[en].next=head[a];
            head[a]=en;
            en++;
        }
        scanf("%d%d",&st,&et);
        printf("%d
",dijkstra());
    }
    return 0;
}